Wind turbines convert wind energy into electricity. The two main types of wind turbines include the horizontal-axis wind turbines and the vertical-axis wind turbines. The two main types of horizontal-axis wind turbines include the upwind horizontal-axis wind turbines (HAWT) having rotating blades upwind of the tower and include the downwind horizontal-axis wind turbines (HADT) having rotating blades downwind of the tower. The two main types of vertical axis wind turbines include one type having rotating blades without lift generating surfaces and include the Darreius-Type having rotating blades with lift generating airfoils (VAWT).
An upwind horizontal-axis wind turbine (HAWT) 10 without guy cables is shown in FIG. 1A, and a Darrieus-Type vertical-axis wind turbine (VAWT) 20 with curved blades and without guy-cables is shown in FIG. 1B. The Darrieus-type vertical axis wind turbine 20 can have curved blades as shown in FIG. 1B or can have straight blades as stated in the original patent of George Darrieus in 1929.
The HAWT 10 has a rotor 12 and blades 14 with lifting surfaces mounted on a horizontal-axis and directed upwind atop a tower 16. Wind energy incident to the blades 14 rotates the rotor 12, and a gearbox and other components (not shown) coupled to the rotor 12 communicate the rotation to an electric generator (not shown) that converts the rotation to electrical energy. To be effective, the blades 12 must be directed relative to the direction of the wind. Therefore, the HAWT 10 typically has a yaw mechanism (not shown) to allow the blades 14 to rotate around the tower 16.
Because the blades 14 are upwind of the tower 16, they must be made of rigid, strong material so they cannot be bent back by the wind and hit the tower 16. Requiring more rigid materials, the blades 14 are more expensive to manufacture and are heavy. In addition, the tower's yaw mechanism must be strong so it can determine the direction of the wind direction and orient the blades 14 into the direction of the wind. Finally, the tower 16 must also be strong so it can support the heavy rotor, gear-box, generator, and other equipment on top of the tower 16. Therefore, the tower 16 requires more materials, is more expensive to build, and is heavy.
Overall, the HAWT 10 as shown in FIG. 1A is a ‘rigid’ wind turbine, requires more materials, is heavy, and has a high center of gravity. In addition, it needs to be oriented to face the wind, and requires a firm foundation or platform. Therefore, it is very expensive to build a floating platform to support the HAWT 10, which is heavy, has a high center of gravity, and requires a very stable platform.
By contrast, the VAWT 20 as shown in FIG. 1B has a rotor 22 that runs vertically from the ground and has curved blades 24 connected at the rotor's ends. This vertical rotor 22 sits on a bearing and gearbox component 26 and drives an electric generator 28. Unlike the HAWT 10, the VAWT 20 is omni-directional and does not need to be oriented into the wind. In addition, the VAWT 20 has a low center of gravity with its heavy components such a gearbox, generator, braking and control system positioned near the ground. Therefore, the VAWT 20 does not require an as rigid rotor 22 as with the HAWT's tower (16; FIG. 1A) to support these components. Example of VAWTs in the prior art can be found in the website of www.ecopowerusa.com.
The HAWTs 10 have been widely used in land-based windfarms around the world. HAWTs have also been used in offshore windfarms in Europe. In FIG. 2A, for example, a first type of offshore HAWT 30A has the conventional components of a rotor 12 and blades 14 supported horizontally on a vertical tower 16. These conventional components rest on a fixed support 32 rigidly affixed to the sea floor 40. Examples of the offshore HAWT 30A illustrated in FIG. 2A can be found in U.S. Patent Application Publication 2007/0040388, published February 2007, and PCT Published Application WO/03/004870, published Jan. 16, 2003.
In FIG. 2B, another type of offshore HAWT 30B also has the conventional components of rotor 12, blades 14, and tower 16, but these components rest on a floating support 34 that is rigidly affixed to the sea floor 40 by cables 36. An example of the HAWT 30B illustrated in FIG. 2B can be found in PCT Application Publication 2005/021961, published Mar. 10, 2005. As these prior art publications disclose many well-known implementation details concerning the design and operation of wind turbines generally, they are all incorporated herein by reference in their entireties.